Current state of the art development of high temperature ceramic superconductors for power applications, e.g., motors, solenoids, magnetic levitation, power transmission and power storage, centers on the encapsulation or cladding of bulk powders of ceramic superconductors in conductive metal sheaths, e.g., silver, to permit rolling or drawing of the composite structure into wires or tapes. The final structures consist of long lengths of high temperature superconductor (HTS) cores surrounded by the conductive metal cladding. Current cladding processes have not generally yielded high quality HTS wires or tapes directly. The rolled or drawn wires or tapes must generally be thermally annealed after fabrication to achieve useful electrical transport properties. Achieving optimum electrical transport properties, such as high critical currents and high critical current densities, in bulk HTS materials has proven exceedingly difficult and is the present focus of worldwide research efforts. Thus, techniques that probe electrical transport properties in bulk HTS materials and especially in clad HTS materials are essential to successful development programs.
Measurement of critical electrical transport properties, e.g., critical currents (I.sub.c), and subsequent calculation of critical current densities (J.sub.c), in clad HTS materials presents a significant challenge because conventional measurement techniques using probes, such as a standard resistivity four point probe, require direct access or contact with the HTS material itself. Direct contact with the HTS core is impossible with a clad structure. The cladding of such a clad HTS material effectively short circuits the standard resistivity four point probe measurement and can lead to the measurement of erroneous values for the critical currents and calculation of erroneous values for critical current densities. Therefore, such conventional measurement techniques are of limited utility.
Accordingly, it is an object of this invention to provide a method for measuring critical currents in superconductor materials, especially in clad HTS materials.
It is a further object of this invention to provide a non-contact method for measuring critical currents in superconductor materials, especially in clad HTS materials.
Yet another object of this invention is to provide an apparatus for measuring critical currents in clad superconductor materials, especially in clad HTS materials.
Still another object of the invention is to provide an apparatus and method for determining the critical current densities in clad superconductor materials, especially in clad HTS materials.